1. Field of the Invention
The present invention relates to film projector elements for selective projection of an image onto a viewing screen mounted on a projector housing or a viewing screen remotely located from the projector.
2. Description of the Prior Art
Film projectors have found wide spread use in the home entertainment, business, and education fields. Projectors may take the form of motion picture, slide, or filmstrip projectors.
A first species of projector is adapted to project an image on a viewing screen remotely located from the projector. Projectors of this species are particularly suited for visual presentation to large audiences. A second species of projector is adapted to project an image onto a viewing screen, defined herein as a local viewing screen, mounted on the projector. Projectors of this second species are suited for visual presentations to small audiences and are particularly suited for visual presentations to one person.
Projectors of both species may be combined with audio reproduction means, such as magnetic tape playback devices, to provide a combined audio-visual presentation.
Projectors which utilize a filmstrip or slides to sequentially present filmstrip frames or slides may be combined with automatic advancing means which advance a filmstrip frame or slide in response to cueing signals recorded on magnetic tape. Such machines are ideally suited for individual programmed instruction.
There is a need for a projector which combines the desirable features of the remote screen and the local screen projector, viz., a projector capable of selective projection of an image onto a viewing screen mounted on the projector housing or a viewing screen remotely located from the projector. As is apparent, such a projector could be utilized for individual or large audience presentations. Prior art projectors capable of selective local viewing screen or remote viewing screen projection have employed various projector elements, such as, a mirror or mirrors to reflect the image onto the local viewing screen, and plural objective lenses.
One such prior art projector described in U.S. Pat. No. 3,447,869 to Szymber provides selective projection to a remotely located viewing screen or a local viewing screen mounted on the projector cabinet. This projector utilizes a cam plate coupled to a pivotable control lever. The cam plate includes a plurality of cam tracks coupled to the projector mirror and to a lens carrier carrying a local viewing screen objective lens and a remote viewing screen objective lens. When the control lever is actuated to a first position the projector mirror and lens carrier are lifted to provide remote screen projection. When the control lever is actuated to a second position the projector mirror and lens carrier are lowered to provide local screen viewing. The control lever actuation force for actuation to the first position is larger than the actuation force for actuation to the second position. In order to minimize the control lever actuation force for actuation to the first position, it is necessary that the projector mirror and lens carrier be of light weight construction.
The projector described in U.S. Pat. No. 3,447,869 utilizes a single condensing lens in association with both the local viewing screen projector lens and the remote viewing screen objective lens. While the single condensing lens may provide adequate illumination efficiency for both the local viewing screen objective lens and the remote viewing screen objective lens, it can not provide optimum efficiency for both lenses.
The present invention seeks to provide projector elements for a film projector which overcome the disadvantages of the prior art. Projector elements are provided in which screen selection is achieved with a single movement control lever to cause displacement of the projector elements with a minimum of lifting of the projector elements. The control lever actuation force is kept to a minimum, and the actuation forces are substantially equal for actuation of the lever in a first direction or a second direction. The present invention also seeks to overcome the disadvantages of the prior art by providing a projector having separate condensing lenses associated with each objective lens to achieve optimum illumination efficiency for both local screen viewing and remote screen viewing.